Refractory keratoplasty is a surgical procedure to alter the cornea's curvature for the purpose of correcting the refractive error of the eye. The procedure can range from producing precise surgical incisions in the cornea to implantation of either a lathe cut hydrogel or human stroma lenticule. This grant proposal is directed toward an investigation of the use of implants for refractive keratoplasty. Hydrogel materials are presently being used for extended wear contact lenses that are high (70-80%) in water content and are very permeable to solutes. Because of these characteristics along with the ability to precisely lathe cut a given power and base curve, the nonreactive nature in the tissue, stability and availability of material, it is an excellent choice as an intrastromal corneal implant. Yet, it is a foreign substance to the body and may not be accepted by the tissue during a long term follow-up. Human donor tissue is biologically the perfect choice as an implant material, but is more difficult to precisely lathe cut, offers a less reliable supply of material and possibly a less dimensionally stable lenticule. The advantages and disadvantages of these implant materials shall be investigated in laboratory animals (rabbit, cat and primate) by their stability and predictability of refraction, corneal curvature, corneal thickness, stromal light backscatter, visual acuity and investigation of the cornea/implant histological ultrastructure, collagen and keratocyte turnover rate, and microbiological challenge response. Also, the hydrogel material's important physical characteristics, such as pore diameter, and water and solute permeability, will be evaluated in six different materials.